1. Field of the Invention
This invention relates generally to microwave ovens. More particularly, it relates to a microwave oven which adaptively avoids interference with a communication device (e.g., a cordless telephone) operating in the microwave frequency range.
2. Background of Related Art
Microwave ovens, familiar to most people, are commonplace in homes and office kitchens. A microwave oven provides a user with the convenience of quick and efficient cooking.
In a typical microwave oven, microwave energy is generated in a special electron tube, such as a klystron or a magnetron, with built-in resonators to control the frequency at a pre-determined frequency. Alternatively, microwave energy for cooking purposes can be generated using special oscillators or solid-state devices. The microwaves generated in a conventional microwave oven are short, high-frequency radio waves (i.e., ultra high frequency (UHF) radio waves) lying roughly between very-high-frequency waves and conventional radio waves (i.e., between 300 megahertz (MHz) and 3 gigahertz (GHz)).
Microwave ovens operate by agitating water molecules in food with the microwave energy, causing the water molecules to vibrate, producing heat. In a typical microwave oven, microwave energy enters through openings in the top of a cooking cavity, and a stirrer scatters the microwave energy evenly throughout the oven.
While useful for cooking, microwave energy has many other types of applications. For instance, besides microwave ovens, microwave energy is used for broadcast radio and television, radar, meteorology, satellite communications, distance measuring, UHF CB Radio, and Mobile Phones, to name a few.
Exposure to microwaves can be dangerous, particularly where high densities of microwave radiation are involved. Microwaves can cause burns, cataracts, damage to the nervous system, and sterility. The possible danger of long-term exposure to low-level microwaves is not yet well known. Nevertheless, the U.S. government generally limits the exposure level to microwave energy to 10 milliwatts per square centimeter, with stricter limits typically placed on microwave ovens. Nevertheless, in microwave ovens, some amount of microwave energy is allowed to, and does, escape through the shielding surrounding the cooking cavity, particularly through the screening in the door allowing visual observation of the food being cooked. This escaping microwave energy can and does cause interference with nearby electronic devices, e.g., a cordless telephone utilizing the same or similar frequency band for the transmission of communication information.
FIG. 5 depicts the operation of a microwave oven 302 in the vicinity of an electronic device, e.g., a cordless telephone system affected by the leakage of microwave energy.
In particular, as shown in FIG. 5, a remote handset 304 of a cordless telephone system and/or its base unit 306 is operated in the vicinity of a conventional microwave oven 302, which leaks some amount of microwave energy. In the given example, the cordless telephone system utilizes a microwave frequency band for communication purposes between the remote handset 304 and its base unit 306. As a result, operation of the cordless telephone 304, 306 can suffer during operation of the microwave oven 302. This is particularly true if the remote handset 304 and/or base unit 306 of the cordless telephone is placed within close proximity of the microwave oven 302 while it is operating, and/or if the wireless communication path between the remote handset 304 and its base unit 306 crosses in a vicinity of the microwave oven 302.
In many instances, the user of the cordless telephone either may not detect the interference caused by the microwave oven (e.g., with error correction compensating for a low level of interference), or may not appreciate the operation of the microwave oven as the cause of a disruption in service between the remote handset 304 and its base unit 306.
Thus, there is a need for a microwave oven which better avoids interference with communication devices (e.g., a cordless telephone) within the vicinity of the microwave oven.